What counts as an ultramarathon?

Any footrace longer than a marathon — anything beyond 42.195km. That is the entire definition, and in practice the category covers events so different from each other that the label says relatively little.

The common distances and formats:

50km — the shortest ultra, and for many runners a marathon with a bit extra.

50 miles (80km) and 100km, both with established world records and championships.

100 miles (161km), the classic ultra distance, typically taking 15 to 30 hours and involving running through at least one night.

Timed events — 6, 12, 24 hours, or six days — where the winner covers the greatest distance rather than finishing first. These produce a completely different discipline, with strategy around continuous movement and minimal stopping.

Stage races across multiple days, such as the Marathon des Sables.

Backyard ultras, a format where competitors run a fixed loop every hour until only one can continue — with no set distance and, by design, exactly one finisher.

What makes them different from marathons beyond distance:

Terrain. Most ultras are on trails, with substantial elevation. A mountain 100km can take longer than a road 100 miles, and vertical gain is frequently the more meaningful number.

Walking is normal, not failure. Efficient power-hiking on climbs is a trained skill.

Eating becomes the limiting factor. Beyond a few hours, performance depends on taking in enough calories, and gastrointestinal distress is among the most common reasons for not finishing. Ultra runners practise eating as deliberately as running.

Checkpoints and cut-offs structure the race, with mandatory kit checks on mountain events.

Crew and pacers are permitted in many races.

Sleep deprivation in the longest events, with hallucinations reported and well documented.

Completion rather than placing is the goal for most entrants, and finishing rates in hard events can be well under half.